In a digital processing device, it is effective in improvement of the performance of a digital processing device to optimize timing in an actual operation for a clock signal as a reference to timing in an operation of a digital circuit. This has been described in Japanese Patent Laid-Open No. 2001-43261, “Digital System, Clock Signal Adjustment Method for the Digital System, and Recording Medium Recording Process Program To Be Executed According To The Adjustment Method” (hereinafter, referred to as Patent Literature 1). It is also described in Patent Literature 1 that it becomes possible to increase the maximum clock frequency of the digital processing device by adjusting timing of the clock signal thereof by using a genetic algorithm.
Adjustment of a clock signal causes an amount in delay of the clock signal to be variable by using a number of inverters and switching an inverter stage number with a multiplexer. In this method, however, it is necessity to have a large number of inverter circuits for adjustment circuit, resulting in that the ratio of an area occupied with the inverter circuits to an area for IC chips becomes very large. Further, there arises a problem that the amount of the clock signal delay is influenced by an LSI operating environment such as an ambient temperature, voltage, or the like. Further, it is difficult to set the timing finely, and it is impossible, in principal, to set the timing at a shorter interval time than the delay time for one stage of an inverter.
As described above, in such a clock timing adjustment method by prior art, there have been problems that the ratio of an area for the inverter circuits to an area for IC chips is large, and clock timing changes because it is influenced by an LSI operating environment such as an ambient temperature, voltage, or the like. In view of these problems, the problem to be solved by this present invention is to realize a delay circuit with high-resolution timing whose circuit area is small, and which is not influenced by the operating environment.